It can be implemented for sure, in fact, it’s already here
- Go to the settings panel
- Turn on “Toggle ruler” under the “Available Toolbox Buttons” section
- Click on the ruler button in the toolbar
- Enjoy the rulers and the small page size indicator.
Note that if you are dealing with responsive layouts and have a set of pre-defined page size to check, you can use the responsive design mode and create the sizes that you need